1. Field of the Invention
The present invention relates to a fixing device, a fixing device control method, and an image forming apparatus, and more particularly, to a fixing device that fixes a toner image in place on a recording medium with heat and pressure, a control method for use in such a fixing device, and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine incorporating several of those imaging functions, which employs a fixing device with a heating control capability.
2. Description of the Background Art
In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of those imaging functions, an image is formed by attracting toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium by melting and setting the toner with heat and pressure.
Various types of fixing devices are known in the art, most of which employ a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip through which a recording medium is passed to fix a toner image onto the medium under heat and pressure.
Those types of fixing devices may be operated with different types of recording media varying in terms of basis weight or mass per unit area, surface properties imparted, for example, by coating material, etc., depending on specific requirements of print jobs being processed. Also, the fixing device can experience varying operational conditions depending on specific applications of an image forming system in which the process is installed. For example, some printers execute print jobs at a low processing speed with an elongated period of deactivation between consecutive print jobs, and others execute a large number of print jobs at a high processing speed sequentially and continuously.
The inventors have recognized that such variations in operational conditions can result in variations in the amount of heat applied through the fixing nip. This is particularly true with a today's power-efficient fixing device that has a heater for heating a fuser member to a regulated heating temperature but no dedicated heater for a pressure member, wherein the pressure member exhibits a relatively low heat capacity and therefore is susceptible to variations in operational temperature. Variations in the amount of heat applied through the fixing nip often take place due to variations in operational temperature of the pressure member, which can result in excessive amounts of heat applied to the recording medium. Inconsistent heating through the fixing nip, if not corrected, would adversely affect quality of the toner image processed through the fixing device, since good fixing performance depends on the ability to heat a recording medium to a consistent, desired temperature sufficient for fusing and melting toner particles through the fixing nip.
To date, various methods have been proposed to provide a fixing process controllable against variations in environmental and operational conditions.
For example, an image forming apparatus may be given a controller that modifies a control parameter of an electrophotographic imaging process based on user-specified information representing properties of a recording medium in use. Alternatively, an image forming apparatus may employ a controller that controls operation of a fixing process based on physical properties of a recording medium, such as surface texture, thickness, moisture content, etc., detected during operation.